Flashcards in Spermatogenesis Deck (22):
What is the general structure and function of the rete testes?
The rete coalesces in the superior portion of the testis to form 5 to 10 efferent ducts, which leaves the testis, entering the head or caput of the epididymis. The rete testis receives drainage from the central, superior and posterior regions of the testicular seminiferous tubules.
What occurs in the seminiferous tubules, what is a special structure of the tubules, and why is this structure important?
Seminiferous tubules provide a unique environment, called blood-testis barrier (BTB), for spermatogenesis. It is a physical barrier between blood vessels and seminiferous tubules. This barrier prevents some proteins and toxic agents from entering the seminiferous tubules.
Why are sperm potentially antigenic?
Since the differentiating germ cells (with 1N haploid DNA) are potentially antigenic, and recognizable as foreign, the barrier sequesters these cells from the blood environment.
How is the Blood-Testes-Barrier formed?
The blood-testis barrier is formed by tight junctions between Sertoli cells.
What is the definition of spermatogenesis?
Spermatogenesis is defined as the process by which spermatogonial stem cells give rise to spermatozoon.
What are the three stages of spermatogenesis, and what happens in each?
Proliferative phase: spermatogonia proliferate to give rise to spermatocytes, but at the same time, maintain their number by self-renewal.
Meiotic phase: spermatocytes undergo meiosis that reduce the chromosome number by half.
Spermatogenic phase: spermatids undergo significant morphological changes and mature into spermatozoa.
What are the three different types of spermatogonial cells and what is the sequence they follow?
Type Ad (dark), Type Ap (pale), and Type B.
The Type Ad spermatogonia can differentiate into another type of spermatogonia, called Type Ap. Type Ap spermatogonia can then divide by mitosis and give rise to Type B spermatogonia, which will further divide to produce preleptotene spermatocytes that enters meiosis.
What is the sequence of cells from Spermatogonia to sperm?
When does the spermiogenic phase occur and what processes happen in it?
Following the meiotic phase is the spermiogenic phase, or spermiogenesis. It is a maturation process by which a haploid spermatid differentiates into the mature spermatid. There is no change in terms of the chromosome number or DNA amount. As the spermatid matures it elongates, develops a tail flagellum and assumes a configuration similar to that of the mature spermatozoon.
What are the four stages of spermiogenesis?
Spermiogenesis is a dynamic process and can be roughly divided into four stages: Golgi phase, Cap phase, Acrosomal phase, and Maturational phase. The spermatid contains a prominent round nucleus, a Golgi apparatus, a set of centrioles and mitochondria. These organelles, with the aide of Sertoli cells, will undergo architectural changes that will transform the spermatid into the mature spermatozoon.
What occurs during the first stage of spermiogenesis?
Large acrosomal vesicles are elaborated by the Golgi apparatus (become the most prominent cytoplasmic inclusion within the spermatids)
The acrosomal vesicle migrates to one pole of nucleus and centrioles move to the opposite end of the nucleus.
The acrosomal vesicles will eventually become the acrosomal cap of the sperm.
What occurs during the cap phase of spermiogenesis?
The centriole continues to extend out away from the nucleus to form the flagellum and in the process it pulls most of the cytoplasmic inclusions away from the nucleus. The inactive centriole remains intact and will be present in the neckpiece of the mature sperm.
What are the primary functions and structure of the epididymus?
The primary functions of epididymis are post-testicular maturation and storage of spermatozoa. Anatomically, the epididymis can be divided into three regions: head (caput), body (corpus), and tail (cauda).
What occurs in the epididymus?
In the epididymis, spermatozoa will develop motility, become capable of fertilization, and go through the final step of maturation called capacitation.
At what point/location in the epididymus are the sperm capable of fertilizing an egg?
Spermatozoa taken from the caput or proximal corpus are generally incapable of fertilization, whereas those from the distal corpus and the cauda are able to undergo capacitation and achieve normal gamete interaction.
Where are the majority of spermatozoa stored?
The cauda epididymidis is the major storage space for spermatozoa, which accounts for about 70% of all the spermatozoa present in the male tract.
How long does the process of spermatogenesis take? How long does each stage take?
In the human, the entire sequence of spermatogenesis from spermatogonia to spermatozoa takes about 64 days. Each stage, from spermatogonia to primary spermatocytes, to spermatid, to spermiation to finish, takes about 16 days.
What is the morphology and location of Sertoli cells?
Sertoli cells are tall, narrow columnar cells that extend from the basal lamina of the seminiferous epithelium to the tubular lumen.
What are the functions of the Sertoli cells?
Act as a supporting matrix for the developing germ cells.
Provide the supporting matrix and nutrition for spermatogenesis
Involve the movement/release of germ cells during spermiation.
Maintenance of blood-testis barrier
What hormones do Sertoli cells interact with and what products do they secrete?
Express FSH receptors
Receive FSH stimulations from pituitary.
Secrete androgen-binding protein, or ABP, which has high affinity to testosterone. This helps maintain the high concentration of androgen within the seminiferous tubules, which is critical for spermatogenesis.
Secrete inhibin, which has a negative feedback on the production of FSH from pituitary.
Where are Leydig cells located?
The Leydig cells are clusters of cells located in the interstitial tissue between the seminiferous tubules.